1. Field of the Invention
This invention relates to a throttle control device for an internal combustion engine, in which the real opening of a throttle valve disposed in the intake air passage of the internal combustion engine is feedback-controlled to a desired opening.
2. Description of the Related Art
The disclosure of JP-A-7-293284 is enumerated as the throttle control device for an internal combustion engine, which is known in the related art. The control device, as disclosed in the Publication, uses the known PID (Proportion Integration differentiation) control arithmetic procedure basically as the control arithmetic processing for feedback (F/B) controlling the real opening of the throttle valve to a desired opening. In order to obtain the amount of activation for a quick valve drive even when the opening deviation (i.e., the desired opening—the real opening) of the real opening to the desired opening is small, moreover, the PID control gain is set variable according to the opening deviation, as shown in FIG. 2, and the PID control gain map is prepared so that the value of the control gain may be large when the opening deviation is small. By thus setting the control gain variable for the opening deviation, the activation amount can be quickly enlarged to reduce the opening deviation even when the opening deviation is small.
However, the aforementioned throttle control device of the related art fixes the control gain which is retrieved when an equal opening deviation occurs. It is, therefore, difficult to control the motor torque such that the throttle valve is quickly driven when a minute opening deviation occurs in the entire temperature range of the throttle valve operation and such that the real opening may not overshoot or undershoot from the desired opening. For example, when the motor temperature changes to change the motor winding resistance according to the running state of the internal combustion engine, the motor current value does not takes an equal value even for the equal value of the motor control voltage. When the equal opening deviation occurs, therefore, the control DUTY value and the motor control voltage value to be calculated by control means are controlled to the equal value by the PID control operation. Even with this control, however, the motor current value is changed by the change in the motor winding resistance by the motor temperature so that the motor drive torque proportional to the motor current is not controlled to the equal value. In short, the motor drive torque to be controlled and outputted when the equal opening deviation occurs is higher at the lower temperature and the lower at the higher temperature.
The motor control line takes the higher gain at the lower temperature, as described above. It is, therefore, general to adapt the control gain so that no control hunting may occur at the low temperature. In this case, the gain of the motor control line is lowered in the operation at the high temperature by the rise in the motor winding resistance. When a minute opening deviation occurs, therefore, the torque necessary for driving the valve is not quickly outputted to delay the response to the real opening (as referred to FIG. 4A). When the control gain is adapted for the quick valve drive at the high temperature, on the other hand, the gain becomes excessive at the low temperature so that a hunting of the real opening occurs (as referred to FIG. 4B). This raises a problem that the PID control gain generally has to be adapted for avoiding the opening hunting at the low temperature while sacrificing the opening responsiveness at the high temperature. Here in FIGS. 4A to 4C: letter L designates a desired value; letter M designates a control response at the low temperature; and letter N designates a control response at the high temperature.